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http://www.newscientist.com/article/mg20327154.300-hippy-monkey-is-a-killer-when-starved-of-sex.html

'Hippy' monkey is a killer when starved of sex

04 July 2009 by Mairi McCleod

DEEP in the Atlantic forests of Brazil lives the muriqui - the world's
most peaceful and egalitarian primate. Or is it? The cuddly reputation
of the "hippy monkey" has taken a battering after a gang of six were
spotted attacking and killing an adult male.

The victim, an old male, died an hour after receiving savage bites to
his face, body and genitals. The observations, published this week in
the American Journal of Primatology (DOI: 10.1002/ajp.20713), show how
lifestyles may dramatically alter the behaviour of a species.
The victim was an old male who received savage bites to his face, body
and genitals

The muriqui's peaceful reputation stems mainly from northern
populations that feed on abundant leaves, and where males patiently
queue to mate with females.

But in the southern population where the attack took place, fruit is
more widely available than in the north, and this may provide a clue
to the assault, says Mauricio Talebi of the Federal University of São
Paulo-Diadema, Brazil, who led the research.

Because fruit is widely dispersed, females detach from the main group
to locate it, making them less available for sex with the males than
in the north where everyone stays together to eat leaves.

Lacking ready mates, males may become frustrated, creating mutual
tension and aggression. Also, muriqui males bond closely for life with
male siblings and relatives. Filippo Aureli of Liverpool John Moores
University, UK, says that this facilitates "gang" attacks, as closely
bonded males are in a strong position to victimise an individual.